text:
On a Boeing 737, can the APU, BY ITSELF, provide enough thrust to move the plane while on the ground?
There are numerous questions and answers about the ability of an APU to provide enough thrust to maintain flight.  In contrast, my question is whether the APU, by itself, provides enough thrust to move the plane on the ground.  This is what motivates this question --
Back in the 1980s I often flew between Bangkok Thailand and Chiang Mai.  It was normally a non-stop.  But on one particular flight, it made a stop at a tiny intermediate airport.  Looking out out the window (passenger window) I saw that the vehicle parking lot abutted the tarmac with no intervening separator.  The parking lot was graveled, and considerable gravel had migrated to the area around the plane.
This seemed to me to be a serious safety hazard for ingestion into the engines, and I wondered whether the APU, by itself, could produce enough thrust to move the plane clear of the gravel.
Thanks.

Yes, I meant "move."  Also, the airport was too small to have a tug.

With absolute certainty, no. The "thrust" is too little by orders of magnitude. Enough wind could get the airplane moving if it wasn't chocked and the brakes were released, but not the APU.

An APU is a gas turbine but not a propulsion engine, it's a power generator (like this one). It produces no thrust at all, all power is used to turn the shaft and is converted into another form of energy, electricity or fluid pressure.

I can't reference to a document, but I can say with reasonable certainty that the answer is no, because like any turboprop or turboshaft, the APU has nearly all of the energy of its mass flow extracted for bleed air, or for torque production purposes for electricity, so that there is little thrust energy available.  Turboprops typically get maybe 10% of the total energy available from the engine as exhaust thrust.
So using that number for an APU in an airplane the size of a 737 that is making, say, 650 shaft horsepower (just an educated guess; the actual number is surprisingly hard to find), it's producing a thrust equivalent to roughly 65 hp statically out its tailpipe, which equates to perhaps 2-300 lbs of static thrust (I recall that it's something like 4lbs thrust = 1 HP in the static case) at most.  That would be if the tailpipe was even optimized for making thrust in the first place (tapered to accelerate the flow), which they are generally not.
So, figure on a few hundred pounds of push at most, probably quite a bit less, which isn't going to move a 737 unless it's on some kind of near-frictionless surface, or in outer space.


text:
What can airline pilots do if they are no longer in the position to fly, career-wise?
I was having a discussion with a friend about the incident in the past days (4U 9525) and more specifically the what could be described as 'Taboo' of Psychological problems among pilots. We came across a few points:

They will only reluctantly admit that something is wrong, since risk losing their Medical (hence being 'grounded'). It will only be easier to loose and harder to get back I suspect after this event.
At least for the younger bunch who might have difficulties they will have substantial debt from training that is difficult to pay off. Furthermore, they will have worked hard to get where they are.
Any airline that does suspect something will most probably not allow them near the cockpit again. Should anything happen the airline will be held to blame, since they did allow him to fly despite knowing of the problem.

This brings up the question: What can a pilot do, career-wise, if they feel they are unable to exercise the profession? It seems pretty cornered to me. Perhaps work in dispatch/ network control was the only one I figured their knowledge could come to use. Switching to the simulator I suspect might also be possible, but not for the younger individuals.

You include a reference to GermanWings 9525, but the only clear link is currently speculative.

@raptortech97: It's official that a doctor had put the FO in question on medical leave. That is not really speculative.

@JulianHzg I guess so. I'm just concerned a link is being implied between the medical leave and crash.

@raptortech97: I think MikeFoxtrot actually did a good job not implying anything unnecessarily.

@JulianHzg yeah, looking over it again it seems fine

A 50 something pilot with a mortgage & a couple of kids in college isn't exactly in a good position to switch to an entry level job in another field.

An airliner pilot is (usually) qualified to fly jets. Some medical conditions mean they can lose that qualification but still hold a private pilots licence on propeller aircraft. I'm not sure if they are permitted to obtain or hold a commercial pilot licence on propeller aircraft but I know a guy who can no longer fly jets but who occasionally flies (unpaid) as FO on a King-Air carrying executives about.

I think a career as a Sim instructor would be the preferred route if you had the experience to swing it.  Also, maybe test pilot stuff?  It might also be possible to work as a consultant to design firms, if you have enough experience.

There are quite some paths, but if you love flying jets, and he certainly enjoyed it, none of them is feasible...

When I worked in the design department of an aircraft company, I had two types of coworkers: Those with and those without a pilot's license. You could easily spot the difference. In aircraft-related engineering decisions it was soon obvious. I mightily preferred to work with other pilots - they would have a much better grasp of "what looks about right" and not pursue hare-brained, outlandish ideas.
See it this way: All managers in car companies have a driver's license, so they have at least some contact with what their companies make. All higher managers where I worked had no pilot's license, and it made work outright awful. They were trained as beancounters, and that restricted their viewpoint. They were simply incapable of telling good engineering from bad.
If you have managed to get a CPL, adding an engineering degree on top is not hard. That is my advice to grounded pilots: Go to engineering school and enrich the workforce with your experience.

You are the first person I've ever known to use the words engineering degree and not hard in the same sentence.

@SteveV. My brother who is a captain on B737 told me once that getting his Commercial Pilot License was murch harder than getting his engineering degree (related to aeronautics). So yes, in this particular case, I can imagine that Peter is right.

As a pilot with an engineering degree (or, perhaps more accurately, an engineer who also flies airplanes,) I found the assertion about it being 'not hard' to be a little questionable, too. Still, this is a good suggestion, assuming one is good with (and enjoys) math and physics. And I completely agree about managers who are not engineers. Avoid those to the maximum extent possible. People who are not engineers making high-level engineering decisions does not usually end well.

The comparison with car-driving managers is a bad one. Unless you're claiming that those same managers who couldn't tell good engineering from bad in an aircraft company would suddenly be able to tell the difference if they worked in a car company, just because they drive a car to work.

@DavidRicherby: That happened really to the CEO of BAe some years ago. He (at the Hannover air show): "That is an interestingly looking airplane!". Journalist next to him: "Your company is making those". Would that happen with car company managers at an auto show? But sounds extremely familiar to me. BTW, the aircraft concerned was the MRCA Tornado, if I recall it correctly. Still a bad example?

Unfortunately, because engineers are good with numbers, they're often bad with people, and because managers are often good with people, they're often bad with numbers. That, sadly, is they way companies work. (Please note the heavy use of the word often - it is a generalization and doesn't apply to your boss.)

@FreeMan: I am intelligent enough to see through the phrases and hot air from management. If you want my respect and my cooperation, you best convince me that your plan has technical merits. The manager I respected most in my career was an Ex-Navy pilot. Yes, he was also good with people, but he knew what he was talking about, and that counted for me. And made him different from most other managers. Often, generalizations mask a deeper truth: Here it is a poor selection process. Trust me, there are enough technical people to fill all management positions. Three times over, if you want.

The car analogy is not correct. There's much more to building vehicles than having a driving licence. But the vehicle industry can also have mangers who think they know all about e.g. mining machine gearboxes  because they have on occasion driven a family saloon. The ones who have Porsches are even worse (according to the spouse, who makes gearboxes).

Pilots are intelligent. They can retrain and become good at some other type of work: aviation mechanic, computer scientist, engineer, law. Some of these fields will pay much better than a pilot career will anyway, so don't worry about the sunk cost of pilot training.
If you are not fit to fly, no amount of bargaining/rationalizing is going to fix that — you've got to move on.
The root cause (psychological problems, in your example) is a red herring. You may have to change careers for many reasons: injury, family, health, etc.

Commercial glider and balloon flights don't require a medical, nor do certain kinds of instrument instruction. Someone who's is healthy but wouldn't pass a first or second class medical can have a career teaching, or flying commercial flights like sightseeing and advertising.

You need a second class medical for flying commercial flights like sightseeing and advertising.

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text:
What should I expect during a first class medical examination?
About 57 months ago I got my first FAA medical, a second class certificate.  I am currently a sophomore in college.  I'm in AFROTC trying to become an Air Force pilot so I wanted to get a first class medical just to make sure that I can (I realize military aviation medicals are even more intense though).
What types of things do they do during an exam for a first class medical that aren't included in the exam for a second class?  Also, if I "fail" one of the tests while being examined for a first class - can I still get a second or third class medical to keep my private pilot privileges?

You can see the requirements for all FAA medicals in 14 CFR 67.
Specifically, Subpart C (67.2xx) deals with second class medicals and Subpart B (67.1xx) deals with first class medicals.
The only difference my cursory read of these regulations revealed is:

x.111 - Cardiovascular. A first class medical requires EKG after your 35th birthday and every year after age 40.

This leads me to believe any real differences are likely in the ME's guidelines for issuing the medical, and I am not familiar with those.
The only other differences relate to duration and requirement for the exercise of privileges.
On your second question, if you apply for a first class medical and for some reason could not qualify for one, you will be denied or deferred even if you could hold a lower class medical (this is also true of a second class application).  The only possibilities at the end of a medical exam are walking out with a medical of the class you applied for or walking out without a medical.  There is no fallthrough to a lower class.
If you have an issue that you believe would inhibit your ability to get a first class medical, an avenue to explore this is through AOPA where you can talk with a doctor and get advice on your ability to pass a medical and support in handling a deferred medical application.

Thanks!  I was worried about the different frequencies I am supposed to be able to hear just cause my hearing's not great.  But since the hearing requirements are identical for first and second class I'm not at all worried.

@KeeganMcCarthy  The only hearing test I've ever experienced at an AME office is being able to hear the doc in normal conversation.

That's how my second class was, too.  But when I took my DODMERB (military medical), I had to wear special headphones and tell them when I could hear certain frequencies.  Even though I passed, it was really hard for me - I was hoping the class 1 FAA medical wouldn't be like that.

I wouldn't worry about getting your first class unless you have a real need for it.  The AF won't look at it and will conduct their own medical assessment of your suitability.

Seconded. I can easily pass an FAA first class but the AF wouldn't even let me be on an aircrew, let alone fly the thing.

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text:
Why is there a difference between GPS Speed and Indicator speed?
I just played with flight simulator and noticed that the GPS shows different speed from the speed indicator in the cockpit. Also, GPS speed is higher than the Indicator. Any Idea why?

tail or headwind?

Acctually, I'm not sure

OP, @ratchetfreak was giving you the answer, not asking you a question. :)

Basically its GFS (ground speed) vs AS (air speed) (with variants IAS and TAS). Or in other words: It's the reason why long distance flights fly high.

The speed indicator in the cockpit shows indicated airspeed. Indicated airspeed is usually different than GPS speed, due to wind and aerodynamic effects.
GPS speed is your speed with respect to the ground. If you are standing on terra firma it reads 0. If it reads 100 knots you will be 100NM away from where you are now in one hour, so long as you keep flying in a straight line.
Airspeed is the speed of the aircraft relative to the surrounding air. So if you are standing on terra firma with 20 knots wind blowing in your face, your airspeed will be 20 knots. If you travel at 100 knots airspeed against a 20 knots headwind wind, your ground speed is 80 knots. If you do 100 knots airspeed with 20 knots tailwind, your GPS speed reads 120 knots.
But even in calm wind conditions the airspeed indicator will read differently than the GPS speed . This has to do with the way airspeed is measured.
Airspeed is measured with a pitot tube. A pitot tube has two pressure measurement ports. One that measures the total pressure $P_t$. This port is facing the incoming airflow. The other measures the static pressure $P$ and is placed perpendicular to the airflow. The difference between the two pressures is called impact pressure (pressure rise due to the airflow impacting the pitot tube) and is denoted $q_c$.
The impact pressure is related to the speed of the airflow the pitot tube is exposed to. If the flow is considered incompressible (which is an acceptable approximation for speeds up to 200 knots) the impact pressure can be derived from Bernouilli's equation.
$q_c = \frac{1}{2}\rho V^2$

$q_c$ is the impact pressure in Pa
$\rho$ is the density in kg/m3
$V$ is the true airspeed in m/s

The airspeed indicator is calibrated for standard sea level conditions, where $\rho$ is 1.225 kg/m3. In reality the aircraft will fly at altitude and therefor the actual density of the air is lower. Therefor the indicated airspeed will be lower as well. For example if an aircraft flies 75 m/s (about 146 knots) at 6000 ft the density will be 1.02393 kg/m3.
$q_c = \frac{1}{2} 1.02393 \cdot 75 ^2 = 2879.8 \textrm{ Pa}$
The equivalent airspeed at sea level for the same $q_c$ is:
$V_{EAS} = \sqrt{\frac{2 q_c}{\rho_0}} = \sqrt{\frac{2 \cdot 2879.8}{1.225}} = 68.6 \textrm{ m/s}$
Your airspeed indicator will read only 68.6 m/s (133 knots) despite the fact that you are moving with 75 m/s (146 knots) with respect to the air.
Conversion of true airspeed to the equivalent airspeed can be done directly by:
$V_{EAS} =V\cdot \sqrt{\frac{\rho}{\rho_0}}$

$V_{EAS}$ equivalent airspeed (m/s)
$V$ true airspeed (m/s)
$\rho$ actual air density (kg/m3).
$\rho_0$ density at standard sea level conditions (1.225 kg/m3)

The effects of the lower density on your aispeed indicator become more pronounced the higher you go. Once you go faster than about 100 m/s true airspeed the effects of compressibility can no longer be ignored and the above no longer applies. Airspeed indicators are corrected for effects of compressibility and therefore don't use the equivalent airspeed but instead use calibrated airspeed for calibration.
$V_{CAS}=a_{0}\sqrt{5\left[\left(\frac{q_c}{P_{0}}+1\right)^\frac{2}{7}-1\right]}$

$V_{CAS}$ is calibrated airspeed
$a_{0}$ is the speed of sound under standard sea level conditions (340.3 m/s)
$P_0$ is the static air pressure under standard sea level conditions (101325 Pa)
${q_c}$ is the impact pressure

The impact pressure is also a bit more complex for compressible flow:
$\;q_c = P\left[\left(1+0.2 M^2 \right)^\tfrac{7}{2}-1\right]$

$P$ the static pressure
$M$ the Mach number

Effectively, the higher and faster you get, the greater the difference between the indicated airspeed and the true airspeed.
For example, Mach 0.8 at 40000 ft in no wind will result in a GPS speed of 489 knots, but a calibrated airspeed of only 242 knots, which is less than half.
Therefore at high altitudes and speeds, the indicated airspeed will be lower than the ground speed / GPS speed, unless you have extreme headwind.

Very thorough answer, but I feel it's too advanced and math-heavy, unnecessary for a casual enthusiast (or even for a professional pilot). It reads more like an aerodynamics textbook than a conceptual overview.

@dvnrrs I tried to write it in such way that when you skip over the formulas the basic concept still comes across. I included numerical values to illustrate the effects described in the formulas and included text blocks that explain what is happening.

You definitely put a lot of effort into it, and it's great information for someone who is interested in that level of detail. For the context of this question though, I think the math should be skipped entirely, and the answer presented instead from a standpoint of what a typical pilot would know or need to know. Links to the more advanced stuff can always be provided for interested readers. Just my thoughts!

@dvnrrs No! Please do not skip the math and explanation. Even though it's more than what was asked for it's relevant, useful, and fascinating, and (as usual on aviation.sx) I learned an answer to a question I didn't even know I had. Definitely filing this one away for reference.

@dvnrrs It may be nice to break the answer into two parts.  One for more casual users and one for more technical users/people who want to keep reading.  That being said, I don't think that this is too bad as it is.

As a physics student, those exponents of $7/2$ and $2/7$ are very interesting. Do you care to explain how they arise?

@DavidZhang these are $\tfrac{\gamma}{\gamma - 1}$ and t $\tfrac{\gamma -1 }{\gamma}$. $\gamma$ is the ratio of specific heats which is assumed to be 1.4 for air.

$q_c$ is also known as dynamic pressure.

GPS speed and the ASI show different values due to how they are measured, and has nothing to do with "wind and aerodynamic effects." I made the edit, and it has been changed back by the original author, even after being approved.

@rbp I (the original author) approved your edits only partially, and edited them to keep the original flow of reasoning. I could also have rejected them and then edit in the parts that I agreed with but I thought it was fairer to reward your efforts by accepting the edit. The difference between ground speed and indicated air speed is indeed because they are measured differently and that has everything to do with wind and aerodynamic effects. I purposely mentioned these two components in the first paragraph and expanded on them in the paragraphs below.

what is the aerodynamic effect?

@rbp The change of dynamic pressure with both speed and density and compressibility effects at high speed are all aerodynamic effects.

Here's a very simple graphic of what you could be seeing:

(source: cadblog.net)
And this is why we land into a headwind rather than the tailwind, since otherwise we would land at a faster speed and require more runway to stop.
GPS measures ground speed, or absolute speed. The pitot tube on the aircraft will measure the speed relative to the airflow around the aircraft.
Here's som helpful graphic from NASA on relative velocity:

Footnote: As Ratchet Freak demonstrates in his equation, you have to of course remember that this is simplifying it as flying straight into the wind and not taking account of the wind direction.

That graphic makes my head hurt, but I cant stop staring at it

Indicated "airspeed" is not a speed. At all.

@JanHudec for the non-pilots or aerospace engineers, care to explain?

@NickT: It is a dynamic pressure, expressed as speed at  which that pressure would occur at sea level at standard conditions. There are already two answers that explain it, so I don't have to.

Anyway, by missing the distinction between true and indicated airspeed this question is misleading. Despite the nice graphics.

The other answers about wind are true, but this isn't what you're seeing in your simulation. What you're actually seeing is the difference between true airspeed and indicated airspeed.
True airspeed is the plane's actual speed through the air. With no wind, this is the same as the plane's speed across the ground. This is what your GPS displays.
The airspeed indicator, on the other hand, is really just a "dynamic pressure" sensor. It works by measuring the pressure of the ram airflow. But as we know, as you climb up into the atmosphere, the air gets thinner - less dense, and lower pressure. This makes the airspeer indicator read lower than true airspeed.
The reason it's done this way is because all of the important aerodynamic stuff that can happen to a plane (like stalling) really is tied to dynamic pressure rather than true airspeed.

@Articuno Because sims usually have wind off by default (for ease of flight); the question didn't mention wind; and because the question's wording suggested a non-expert who wouldn't know about IAS.

@Articuno (Also I write software for professional flight simulators and am very used to fielding questions about sim behavior from people of all types. Call it professional intuition.)

Gonna try give as simple an answer as possible, but speeds in aviation takes a bit to get your head around....
The cockpit airspeed indicator (ASI) measures indicated airspeed, or IAS, measured in knots. But IAS is technically not a speed at all. It can be thought of as a measurement of the pressure of the air molecules flowing over the wing.
IAS is the most important speed because if the pressure of air molecules going over the wing is too low you'll lose lift and stall. More speed though means more pressure.
At high altitude, there are less air molecules, so less pressure on the wing. Therefore, to keep the same pressure on the wing (i.e to keep the same IAS), you need to go faster. True airspeed (TAS) measures how fast you are actually going. In flight it will be higher than the IAS. TAS does not care about the pressure over the wing - it's the speed through the air.
Groundspeed (GS) is simply the TAS with the effect of wind added. Groundspeed is the speed of aircraft in relation to the ground. If you have a TAS of 200kts, and a tailwind of 50kts your speed over the ground will be 250kts. This is the speed the GPS will show.

Indicated airspeed is an approximation of the plane's speed in the air. Wind can cause the true airspeed to differ from ground speed (what the GPS shows).
To convert it to ground speed you need to know the wind speed and add them.
$$\vec v_{air}+\vec v_{wind}=\vec v_{ground}$$


text:
How do I get attention on a busy radio channel?
As I understand it (I'm not a pilot), radio communications are a more-or-less first come first served proposition. If I'm in busy airspace with near constant communication between ATC & aircraft, how do I break in to make contact with the ATC for whatever purpose necessary (establishing comms to enter airspace, or whatever the situation may be)?

Listen for a gap, or try to anticipate it, jump in, be quick, and get back off.

Start shouting that there is an emergency.

As Ron commented, the basic answer is that you try to anticipate when a short gap is going to be, and jump on before someone else does. It sounds a bit daunting, but it actually works out pretty well in practice.
That being said, it's not exactly first come first serve. ATC tends to prioritize talking to the aircraft which need the most immediate instructions. So, an aircraft on final is going to get more priority than one which hasn't even entered the airspace yet. Even if you manage to get your request in, if the controller has a more immediate issue to address, you may get completely ignored. Sometimes they'll come back with "calling approach, say again" or sometimes you just have to try again later.
Either way, it's usually not too difficult to stay out of trouble long enough to get someone's attention. If you're IFR or have already made initial contact, you can probably just continue on your path and you'll eventually become a big enough priority for them that they'll call you if you still haven't a chance to get a word in. If you're VFR and haven't made initial contact, you can probably just avoid the airspace for a few minutes.

Thanks, all! I give Bret the nod for the awesome first name, and for garnering the most upvotes.

@FreeMan what's so special about my name?

@BretCopeland I'd wager FreeMan's real name is Bret. ;-P

@SnakeDoc - winner, winner, chicken dinner!  :)  With 2 "t"s though.  :)

Sometimes if it's really crazy and you're VFR, you end up circling just outside the airspace waiting to make the call.  :-)

Key up the mic and state:

Who you're contacting (e.g. Seattle Approach)
Who you are (e.g. Skyhawk 1234)
Where you are (e.g. 5 west of Bremerton)
Your altitude (e.g. 5500)
Your request (e.g. VFR flight following to Renton)

If the frequency is really busy, some people will substitute #3, 4, 5 with "request" (e.g. "Seattle Approach, Skyhawk 1234, VFR request"). Once the controller responds the remaining details can be filled in.

I think its important to mention that you should say "VFR request" in these circumstances in order to reduce ATC's workload. When you first call up and say your tail number and 'request', the first thing the controller has to do is decide if he is required to provide separation services for you. By saying "VFR request", you are letting him know that you are maintaining visual separation, and he will appreciate it.

The trick is to let them know that you want to talk to them as efficiently as possible. That way, they can ask you when they're ready for you.

The first thing to get clear is: who are we talking to here? a tower? an ARTCC? what?
In my experience the biggest problem can be trying to reach a busy tower for a small or medium-sized airport. In other situations, usually ATC calls you, not the other way around. For example, if you request vectoring, you only have to do it once; after that they call you.
If you are trying to reach a tower and they are tied up, it can be a real problem because as you get closer to the airport you need an answer. In one or two cases I have actually had to circle to wait for some chat head to shut up so I could talk to the tower and get instructions for an approach.
Commercial flights have this problem less because they are operating on filed flight plans, so the tower is ready and waiting for them.
Another serious problem is when you are in the pattern on downwind and the tower is too busy to give you a landing clearance. In this situation all you can do is to keep flying downwind. Sometimes it gets ridiculous. I have flown literally miles downwind waiting for clearance to turn onto final, which then turns into this loooooong 5 mile final.
If you fly downwind too far, you might even have to leave the pattern completely and start the whole process all over again, although this has never happened to me.


text:
Where does ice collect first on a wing in flight and why?
I've seen some reports that say ice forms on the back half of the wing and on the outside edge of the wing (the part furthest from the body) before it will form anywhere else.  I'm wondering if this is true?  Where does ice first form on a wing (in flight) in icing conditions?

"Icing conditions" is a pretty vague term that encompasses a lot of various situations that can cause airframe icing (AOPA pdf report, so it's hard to have one definitive answer. That said, you can expect to accumulate some degree of ice when flying through moisture (clouds, rain, etc) when outside air temperatures (OAT) are near or below 36°F / 2°C. Also as a rule, an aircraft's tail will likely accumulate ice faster than the wing in all conditions.
Flying through very cold temperatures (-15°C -> -40°C)
When flying in clouds and rain at the very low end of the icing spectrum, the most likely form of accumulation is rime icing. This primarily forms on the leading edges of wings and tail surfaces, starting (in most cases) with the tail, and looks (initially, at least) a lot like frost. It can create pretty bizarre structures and is pretty easy to spot. Rime ice is (as far as I have seen or read) not going to accumulate anywhere but on leading edges (wings, nose, engine nacelles, tail) as those are the only parts of the structure impacting the relative wind. Either way, it is highly detrimental to your wing's aerodynamic health.
Rime ice can sometimes form 'horns' that start to grow in a V shape forward off the wing, but only in what I imagine are considered severe conditions. The FAA states that rime "typically occurs with temperatures between -15° C. and -20 ° C".

Flying in relatively warm temperatures (2°C -> -15°C)
At warmer temps, the most likely form is clear ice, which is basically like having solid water ice form around the leading edges - again, wings, tail surfaces, nose, engines. It pretty much follows the shape of the leading edge of surface it freezes onto, but it's heavy and still messes with your aerodynamics. Again, like rime, it's freezing more or less on impact (but with larger droplets) wherever the relative wind strikes the airframe.
In some unusual conditions, aircraft can encounter precip known as Supercooled Large Droplets (SLD); these are cold enough to freeze but not on impact, causing a form of icing known as runback ice (FAA pdf). In FAA tests, "ice shape simulations were found to cause substantial penalties to the aerodynamic performance" of multiple NACA airfoils. Runback ice can accumulate pretty far back along a wing, making it difficult or impossible to dislodge using heat or boots (supposedly TKS fluid protection can mitigate this). It's scary stuff.
The FAA states that "Clear ice typically forms when temperatures are around 2° C to -10°C [but] more hazardous clear ice shapes [...] tend to form at temperatures closer to 0°C".

Flying in medium temperatures (-10°C -> -15°C)
When flying in the middle of the temperature range, aircraft wind up accumulating mixed ice, a combination of rime and clear. According to the FAA, "Mixed ice is most likely to form at temperatures between -10° C to -15° C". It is basically as terrible for aerodynamics as rime ice, and pretty much just as heavy as clear ice. No fun.

Resources:

Wikipedia
AOPA Safety Advisor
FAA Safety course on icing types
FAA Safety course on SLD

"Also as a rule, an aircraft's tail will likely accumulate ice faster than the wing in all conditions."  Do you have a reasoning, or source to support this?

Yeah, the AOPA document mentions it. The thinner the airfoil the faster ice accumulates, and the more susceptible the airfoil is to the negative effects. Plenty of accident records with tail plane icing causing a tail stall, leading to a deep stall.

Thanks! I get the second argument, but why would a thinner airfoil accumulate ice faster? Is it because it has less thermal mass (also because the wing is filled with fuel?)?

I think it has to do with the thickness of an airfoil changing the air mass striking the surface around the stagnation point although I admit my aerodynamics knowledge is not mathematical enough to explain why. @PeterKämpf may know what's up.

@egid Great answer. For the most "common" balance distributions (AC behind CG), wouldn't the tail stall actually cause a violent pitch-down instead of a deep stall? ("Classic" scenario: High wing, conventional tail aircraft extending flaps, moving CP aftwards, increasing the downwash on the stab, stalling it, pitch-up moment from stab decreases -> aircraft pitches down -> angular pitch velocity serves to deepen the stall of the stab -> da capo al fin)

Haha, yeah. Late night, not thinking straight.


text:
How can a tug be referred to as company?
I was listening to some [REAL ATC] MD-80 DELTA CRASH at LaGuardia Airport and noticed something just after 8:41. My question isn't about the accident, but actually about a request to the LaGuardia Tower from Tug1 (or Truck1, it's not clear, although the CC calls it Tug1 it sounds like Truck1) where the tug asks "Tug1 at company, we can cross Papa?"
I understand that the term company is used during ATC communications to tell one plane of a company (such as American Airlines) that they are talking about another airplane from the same company.
But how can a Tug/Truck be referring to a place as company?

Not sure how to interpret it, but I would say the comm is "Truck 1 and company ..."  Perhaps it is a tug with a plane attached?

The other thing you'll hear often if you listen to large airports, there's Tugs and Super Tugs. Generally the tugs only work for the company that they are run by. They aren't just general Tugs. The latter of which can move larger planes neither of them really go fast as all of their gearing is set for torque and they are very heavy.

I just saw BowlOfRed's comment, and listened to it again and I could make it out this time as "Tug 1 and Company". So, basically, when used with vehicles, using "and company" will often indicate that there's more than one vehicle in the group(or possibly aircraft in tow), and whoever's being addressed is in charge of talking for them. Just like when a flight of aircraft is flying or taxing, whoever's talking for the flight, that callsign is used for the whole group.
For other examples of "and company": During snowplow operations, usually you'll just have 1 driver in a group talking to Ground/Tower for that group, and they're also in charge of reporting when all their group is clear of runways or other movement areas. Other times, it's when airport operations is escorting(via vehicle) other vehicles on the airport, from survey crews to construction crews.

OK, I hear it that way now as well. Good catch.


text:
What do you call the portion of a tail-dragger takeoff when the tail is in the air?
During a take-off roll out down the runway, in a tail-dragger airplane, what is the period of time called where the plane is level, with the main gear still on the runway, but the tail has come up off the ground and before you pull back on the stick to begin climb-out?

There is no term (that I am aware of) referring to only the portion of the takeoff while the tail is off the ground.
In general, the attitude where just the two main wheels are touching the ground is called "two-point." Likewise, with the tail wheel also on the ground, it is called "three-point."
Specifically, a two-point landing is sometimes called a "wheel landing".
Source

When I first wrote the question, I was thinking it was maybe 'on the step', as in a water-borne take-off. After actually doing some research, I've come to the conclusion that it isn't named, mostly because a tail-dragger pilot is more concerned with maintaining the straightline of the rollout (vice ground looping) than naming a portion of the take off.

Those were my thoughts exactly.

fooot could you maybe add a line to your answer stating that there really isn't a 'name' per se? I'll accept it then.


text:
Where can I find data tables for lift and drag coefficients of airliners?
I'm teaching an introductory course in fluid dynamics and I'd like to show some "real" data regarding drag and lift forces on an airfoil. It is easy to find data on the geometry of typical airfoils, but I was not so lucky with $C_L = f(airfoil, Re, i)$ and $C_D = f(airfoil, Re, i)$ ($Re$ is the Reynolds number and $i$ the angle of attack). I'm looking for that kind of diagram or data :

Data for commonly known aircraft would be great (B737, B747, A320, A380).
Thanks.

My first thought was: Abbott-Doenhoff. They wrote a book with lots of measurement data, and you can find it here. Of course, this was all long ago, but public data for the airfoils of today's airliners are not published.
A lot of data is also freely available in old NACA and NASA reports, however, you need to know what data you want to search for it efficiently.
If you want to focus on glider airfoils, the Stuttgarter Profilekatalog would be my next source, but unfortunately there are still people who want to make money from it even though the work was financed with public money. This is also quite old, and more modern airfoils from Delft University are similarly restricted.
Another great source is the UIUC airfoil database, but here the focus is on section data and not on polars. But it contains many useful links with airfoil data.
And then there is always XFOIL: Feed it with the coordinates, and you get very good simulations of what a wind tunnel would measure, at least as long as most of the flow is still attached. Lots of plotting functions will help to uncover what is going on in much more detail than any wind tunnel data could ever hope to do.

Thanks (+1). Abbott-Doenhoff is a great reference. I was aware of xfoil but I'm still struggling with it since yesterday (it's not that user friendly !).

@cjorssen: XFOIL is at its heart a console application (it was written first in Fortran on a Micro Vax), but it will print out a list of all possible commands when you type "?". Also, the documentation is quite useful. I guess you need to gain a few more days of experience.

I found a web site (mostly in French, but data are language agnostic!). Calculation were made with XFOIL. This is typically what can be found there (with data text file).

Quite an interesting find! Only a few airfoils look "normal", most are very unusual. The same goes for the choice of Reynolds numbers. A pity that the page has so little background on them.

Is the first graph showing that, for most of the Reynolds numbers, there's a regime where Cd decreases with increasing Cl (assuming that Cx=Cd and Cz=Cl)?  That doesn't look right...

It’s a text book and as such not quite freely available, but Obert‘s Aerodynamic Design of Transport Aircraft has a lot of surprisingly accurate data (including e.g. 777 drag polars).
Another source: Modelled from independent analysis and maybe not necessarily provable, but there’s some detailed estimates on 787 characteristics published here.

I think if you try with this site may be you can find a data that you need . http://airfoiltools.com/airfoil/details?airfoil=n0012-il

While a bit dated with respect to modern transport aircraft, Fluid Dynamic Drag and Fluid Dynamic Lift by S. Hoerner has a ton of data on just about every aspect of interest.


text:
How were MH370 debrises found in different and far locations?
After the start of the search for missing Boeing 777 several debrises were found in several locations (Réunion island, Mozabique, Mauritius, South Africa, Madagascar, and Tanzania).
All the debrises were positively linked to a Boeing 777 plane and thus, to the MH370 flight.
My question is that how does a single plane have several debrises in such far distances? Was it flying and losing its parts in the duration of its flying?
Also, the debris found in South Africa was found in its southern coast. Does it mean it was the plane's last location and it crashed there? If yes, why has not anything more been found there?
Note: It's easy to say the plane reached South Africa at the end. Because when a plane flies from Malaysia and goes westward (just like the MH370 flight), it first reaches Mauritius, then Réunion, then Madagascar, then Tanzania (shifting the direction), then Mozambique, then South Africa.

According to Wikipedia "The location of the discovery was consistent with models of debris dispersal 16 months after an origin in the search area then in progress off the west coast of Australia"

Oh, so the debris moved with water. But why they weren't discovered when they had not moved yet?

As usual due to a chain of events, mainly "lack of official information in the days immediately after the disappearance"; "transponder no longer functioning"; "Countries were reluctant to release information collected from military radar" and "it left radar range"

And why did they search the waters in west of Australia? It wasn't relevant to the path of the plane which was westward when it stopped communicating.

It was done according to the information known at the time of the search. This information changed/improved with time

The oceans tend to be fairly large. The Indian Ocean is 27 million square miles in area (70 million km2). For comparison, the US is 3.5 million, Alaska included. Searching the Indian Ocean is at least eight times the job that searching the entire US would have been.
Actually, more like eight hundred times. You can fly over land at 500 knots and descend to look closer when you find something. Underwater, you have to search at 5-10 knots to get best sonar performance. Then you don't immediately see if it's plane debris, an old shipwreck, or illegally dumped trash. You have to summon a ROV mothership to bring and dive that 2-knot machine to the bottom.
Where the floating debris was found doesn't indicate if the plane has actually crashed in that area. Currents can carry it thousands of miles. We can say with certainty that the MH-370 diverted West, and reached the Indian Ocean, because otherwise debris would've washed East of the Malay Peninsula, in the South China Sea. Where exactly in the Indian Ocean remains undetermined as of 2023. Remember, it's 8 times the area of the US.
The actual crash site can only be positively determined once debris is found on the bottom.

Why diverted East? The Indian Ocean is at the West of Malaysia.

West, I meant West. Fixed.

If you are interested in what happened to MH370, it would probably be a good idea if you read all searches and studies that were made since it disappeared (the real ones, not the conspiracy theories, of course). The Wikipedia page on the topic is probably a good starting point.
Most of the evidence points to the aircraft having crashed into open ocean West of Australia.
The aircraft then disintegrated into many different pieces of various sizes, some of which kept afloat. Winds and currents then carried them away to the East coast of Africa (and islands on the way) where they were discovered, recovered and identified.
Given the great distances, and given varying sizes and shapes and buoyancy, not all pieces ended up in the same place, they were spread out over quite large distances.
While there was a lot of confusion initially on the trajectory of the aircraft (which led to searches in many different places), it is now clear that after turning back and crossing Malaysia, the aircraft then veered South, and flew for many hours before running out of fuel and crashing. This was estimated from analysis of ACARS data received by satellites, where Doppler shift and round-trip-time information yielded speed and distance (from the satellite). This has later been confirmed (with apparently higher accuracy) by analysis of disturbances in Wsprnet transmissions at the time.
The initial confusion, lack of transponder data, and limited radar data, means that initially, a lot of time was lost looking for the aircraft in places where it wasn’t. When it became clearer where the aircraft was, the possible area was still extremely large. While many overflights took place in that area, identifying relatively small pieces floating on the ocean, already dispersed over a large area, is very difficult. It’s not like there were full wings floating on the ocean with a beacon on them, or bright orange or yellow liferafts.
If you consider AF447, remember that in that case:

The actual flight path was pretty well known;
Their last known position was very close to the actual crash site (last position sent at 2:10 UTC when the crash occurred around 2:15)

In that case it still took about 36 hours to find signs of the wreckage, and it was already spread over 5 km. So you can imagine what happens if you get that area to search a week after the aircraft has disappeared, and the area to search is soo large that it’s materially impossible to cover it in a timely manner.
I believe there is still debate on how the aircraft “landed”, I.e. whether it was a somewhat controlled ditching (in which case most of the aircraft would have been intact and would quickly have fallen to the bottom of the -very deep- ocean) or if it really crashed (which means a lot more smaller pieces, but a larger possibility of floating debris), but in any case, the delay and the size of the area make locating any pieces in the open ocean extremely difficult.

Why did the aircraft turn back and flyed twoard the south for many hours? Didn't the pilot know the flight path?

@SnackExchange I think the pilot was likely dead or incapacitated. Think fire on board.

@CareyGregoryisonstrike Well, pilot is not alone. What about the co-pilot?

@SnackExchange what everybody thinks but the Malaysians won’t accept is that it was the captain who orchestrated the whole thing. Either incapacitated the other pilot or locked him out of the cockpit, probably incapacitated the whole cabin by hypoxia, disabled the transponder, turned back towards the origin airport (so it doesn’t look too suspicious), then crossed Malaysia, reached the Western tip of Indonesia and headed south towards a place with no radar coverage, no population, deep oceans… it was all planned and rehearsed.

Then what was the captain's motive to do this? He also lost his life

@jcaron: Advancing this as a hypothesis is sensible (although there is not much hope of proving or disproving it) -- but claiming that it is "what everybody thinks but the Malaysians won’t accept" elevates it to a conspiracy theory.

@SnackExchange the prevailing theory is that it was a suicide, related to his state of mind following his divorce. Sadly, this is not the only case of a pilot committing suicide and killing a few hundred passengers and crew with them. The most obvious case is Germanwings flight 9525 where the co-pilot voluntary crashed an A320 into the Alps. But there are a number of other instances where pilot suicide is suspected while not established with certainty.

@A.I.Breveleri while not established officially, I don’t think there is any other valid theory which explains the whole sequence of events, especially given that the captain rehearsed the whole thing on his home simulator (initially denied by Malaysian authorities, but then confirmed several times by several different sources, including Australia’s ATSB and Malaysian authorities themselves).

@SnackExchange If a fire broke out on board, couldn't be extinguished, and produced enough smoke and CO to disable the pilot, then it would do the same to the copilot and everybody else. After all, the pilots only have about 15 minutes worth of O2. A lithium battery fire in the hold could produce the entire sequence of events this plane went through.

Flying to random places in FSX is a common pastime, and an ATP doesn't need sim practice to fly a particular route. Hijacking is the hard part. The theory is plausible. But subtle incapacitation - slow loss of consciousness from CO2 or CO exposure - has also caused a number of similar incidents.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How do I calculate this question? mass and balance
If we start with $Total\ Weight = 2,850\ lbs$ and $CG = 101.67\ in$, then add $400\ lbs\ @\ 97.8 in$, then how much would the Center of Gravity move?
How can you calculate this?

I assume  97.8 is in ... inches? Same for CG?  An important part about calculating things like this is to be clear on what units you are using.

i do not know but i know the answer is  -0.47  how its calculate? thanks

The basic equation is $Weight \cdot Arm = Moment$, which also means that $Arm = \frac{Moment}{Weight}$.That is all you need to work through these problems.
Calculate your starting moment:
$2,850\ lbs \cdot 101.67\ in = 289,759.50\ lbs/in$
After you add 400 lbs, the new Moment is:$(2,850 \cdot 101.67) + (400 \cdot 97.8) = 328,879.50\ lbs/in$
And the new total weight is:$ 2,850 + 400 = 3,250\ lbs $
This produces a new CG of:
$\frac{328,879.50}{3,250} = 101.193\ in$
The difference in CG is:
$101.193 - 101.67 = -0.477\ in$
Or, doing this all in one big equation:
$$
\frac{(2850 \cdot 101.67) + (400 \cdot 97.8)}{(2850 + 400)} - 101.67\ in = -0.477\ in
$$

What is the calculation is telling us? What is the meaning of 400lbs @97.8 in? And what is the meaning of that -0.477 in?

@AirCraftLover: Information on Weight, Arm, Moment, CG, Weight&Balance calculations are readily available from multiple sources and are a basic part of pre-flight planning.   I cannot possibly summarize it in a comment response.


text:
How do I calculate this question? find the position of the centre of gravity in %
Find the position of the centre of gravity in % of the MAC (mean aerodynamic chord) if the distance from the datum to the LEMC (leading edge of mean chord) is 13 meters, the distance to the TEMC (terminal edge of mean chord) is 19 meters and the distance from the datum to the centre of gravity is 15 meters?

How far have you gotten so far?  Show your work.

I'd know exactly

How is calculating?

@EnkiSumerian, you use to many abbreviation. You should put clearly. Provide with drawing or picture as well so it clear.

I believe that the Length of the Aerodynamic Chord is $19\ m - 13\ m = 6\ m$, and that the CG is $2 m$ from the Leading Edge of the Mean Chord (LEMC).
Therefore, I believe that the CG in percent is:
$$
\mathrm{\frac{CG}{Length\ of\ Chord}} = \frac{CG - LEMC}{TEMC - LEMC} = \frac{15-13}{19-13} = \frac{2}{6} = 33\%
$$

@abelensky: In a wing, where the length of chord we measure? Is that At the tip? At the middle? At the root? or where?

The key term is Mean Chord, meaning average chord.  If the wing edge is straight, you can just take the middle.  If it is a curved, sweeping shape, you may need to do a calculus integral to get an exact answer.  In this example, the LEMC (Leading Edge of Mean Chord) is at 13.  So part of the leading edge may be less and part may be more, but the average leading edge is at 13.

Thank you my friend for the nice explanation.


text:
Restricted airspace and lower limits
I am a new UAS pilot who will be flying agricultural fields. Naturally, my first flight location is close to a restricted airspace for military practice. I want to make sure I my flights are compliant.
R-6904A is listed as having a lower limit of 150' AGL.
If I stay under 150' AGL, then I am not technically entering this restricted airspace, correct? Would I need to contact or notify anyone about my intentions to fly if I ensure I never exceed 150' AGL?
There are additional restrictions nearby in zone R-6904B. Here, the restrictions list as starting from the surface. I will never need to enter the area controlled by this restriction, so I should be good to not notify anyone about my flights, right?
I appreciate the help.

I would notify ATC anyway. I mean, there's no reason not to, right?

@MichaelHall If ATC knows you're there, they can warn you about other planes, and warn other planes about you. And air traffic controllers would much rather be talking to you than not.

@MichaelHall ...I somehow completely missed that this was for a drone. Ignore me.

No worries!  I was kinda wondering where you were coming from...  ;)

R-6904A is listed as having a lower limit of 150' AGL.
If I stay under 150' AGL, then I am not technically entering this
restricted airspace, correct?

Correct.

Would I need to contact or notify anyone about my intentions to fly if
I ensure I never exceed 150' AGL?

No.

There are additional restrictions nearby in zone R-6904B. Here, the
restrictions list as starting from the surface. I will never need to
enter the area controlled by this restriction, so I should be good to
not notify anyone about my flights, right?

Right.
Added info -- the airspace in and near these restricted areas is Class G airspace up to 1200' AGL.  If the airspace at the altitudes where you intended to fly were other than Class G, then under FAR 107.41 you would need to obtain prior authorization from Air Traffic Control (ATC) before flying your SUAS there (e.g. on-line authorization via the LAANC system), regardless of whether or not you were flying in a restricted area.
Link to sectional chart showing this area (look near the top of the displayed area)


text:
How do planes descend for landing?
I fly occasionally  on a pretty short route on a turboprop (DHC-8). When the airplane descends for landing, I can look through the window and see the ground below getting closer over time. However I can't really tell what the pilots do to achieve that. I know that turns make you lose altitude, but it's very clear to me when the airplane makes a turn, so let's count that one out. So we're basically left with:

Slight nose-down attitude
Reduction of engine power
Combination of both

The reason I'm asking this is that during descent I do get this sensation of going down. However, during that time I cannot really see what the pilot did to achieve it. The nose-down attitude might be too minor for me to actually notice (I do not notice a slight nose-up cruising attitude to be honest). I hear a slight reduction in engine power a few times during a descent, but the feeling of going down and the audible noise reduction are separated in time. Is it that it takes time for an airplane to reduce speed (and as a result, descend) when you reduce engine power?
One additional question: I guess that with all the electronics in the cockpit pilots just set a target altitude or rate of descent, and then the airplane systems apply the correct measures to achieve this. How does the airplane know how much to reduce engine power and/or pitch to achieve this exact rate of descent?

You'll receive answers here, but if you are interested in discovering more, you may want to read from pilot books, like the chapter "Descents and descending turns" (page 44) of Pilot's Handbook of Aeronautical Knowledge. Altitude is overall controlled by the thrust amount from the propellers, so descending is usually a matter of decreasing the power or the propeller blades pitch. But as usual there are variations and specific cases (you want to descend more quickly), and there are gliders...

Start by reading this answer and transfer it from ascending to descending (= add less energy from the chemical bucket per time than what is needed for level flight).

See How to perform climbs and descents?

If the pilot reduces the airspeed while he increases the rate of descent, you will not notice any change in pitch attitude when the aircraft descends. With jets you should be able to hear a change in engine pitch when thrust is reduced. Turboprops run their engines at constant speed, and a reduction in power here means a reduction in propeller pitch. This causes the propeller noise to change, but this change is harder to discern. With a little practice you should be able to hear the slight drop in propeller noise which signals the begin of the descent, though.
Gliders control their sink rate by flying in rising or sinking air, and additionally by flying slow (and near their minimum sink rate) or fast. To descend quickly, they can open speed brakes and/or sideslip. My favorite for a fast descent is to spin the aircraft, but airliners do not use this option.
In order to produce the necessary lift to keep the aircraft in the air, the pilot picks a combination of speed and angle of attack at which lift equals weight. Other combinations would result in an accelerating vertical speed and are only used in transitions from one flight state to the next.
To arrive at the aircraft's pitch attitude, you need to add the flight path angle to this angle of attack. If the plane descends with a flight path angle of -3° and the pilot reduces speed such that he needs to increase the angle of attack by the same 3° to produce the same lift, the resulting pitch angle of the aircraft would stay the same.
Normally, the correct answer to your question is 2. Reduction of engine power. But the other answers are also correct: If the speed is held constant, the attitude has to be reduced by the desired flight path angle change. Note that this is achieved by reducing thrust alone. If the pilot wishes to descend really fast, he might move to answer 3. Combination of both as in this answer.

With the constant speed props on the DHC-8, a power reduction alone, evidenced by a reduction in torque and N1, may not be readily detectable to the uninitiate. This would not be the case in jet aircraft.

OP asked about airplanes, and you switched to aircraft. gliders work differently.

@JonathanWalters: Good point! I missed that detail.

@rbp Gliders are airplanes, just not powered ones.

@reirab  "Normally, the correct answer to your question is 2. Reduction of engine power."  I tried that in my glider and nothing happened.

The sequence that student pilots are taught is power, attitude, trim. Let's break down those three things:

Reduce engine power by closing the throttle. If you close the throttle partly, you get a powered descent; if you close it completely, you get a gliding descent. Airline operations typically prefer powered descents, mainly because turbine engines are very slow to add power, and you might need to stop descending at short notice (because the terrain is about to back into you). This lets your speed decrease to the desired descent speed (which is typically somewhat less than the cruise speed). While the speed is decreasing, you need to keep backward pressure on the stick to stop the nose dropping.
Once you've reached the correct speed, pitch the nose down to the descent attitude, to keep the speed constant. With the nose too low, the speed would increase, but the rate of descent would be too great, and would keep increasing. With the nose too high, the speed would decrease, which means the wings produce less lift, again causing a high rate of descent (and probably a stall). The combination of engine power and attitude together determine the airspeed and the rate of climb or descent.
Trim the aircraft. This means setting up the control surfaces so that the attitude is stable, and it's quite a big topic in itself, because different aircraft have different ways of trimming.

As for your supplementary point about autopilot and autothrust, the electronics don't actually need to know how much to change the power or attitude to achieve the desired effect. All they need to know is which direction to go (more or less power, nose up or nose down). At its core, the logic is very simple: airspeed too low -> nose down; airspeed too high -> nose up; rate of descent too small -> reduce power; rate of descent too great -> increase power. Because computers think in very small timescales, they can make that decision many times per second, so they never deviate far either side of the desired flight parameters.
Now in fact, it's a little more complicated than that, because the control loop needs to be tuned so it doesn't overreact to small changes, to cope with the delays caused by inertia and drag, and so it doesn't overshoot the target continually. There's a whole branch of engineering called control theory about this kind of system. But fundamentally, it knows how big a change to make by watching the effects of the changes it has made so far.

There are two different ways to climb or descend:
Constant rate climb or descent:  using a constant power setting, the pilot applies pressure on the stick to set a desired attitude for the climb or descent.  This is cross referenced against the vertical speed indicator (VSI) once the climb is established and adjustments in pitch attitude will be made to hold the aircraft at a desired rate of climb or descent.  Trim will also be needed to alleviate elevator pressure as the speed of the aircraft will decrease in a climb and increase in a descent.  Very rapid descent rates will also require a large reduction in power to avoid exceeding Vne or overspending the engine, if a fixed pitch propeller is used.  To level off at a new desired altitude, elevator pressure must be applied to level off the nose and terminate the climb or descent.  Again trim will have to be applied as the aircraft is returning to its cruise airspeed.
Due to the excessive control inputs and trimming, this type of climb is not preferred by pilots who hand fly the airplane.  But it can be popular with aircrews using an autopilot when descending, as you can turn the potential energy you gained climbing to altitude into additional airspeed, allowing for a faster arrival to their destination; the autopilot can easily cope with the grunt work trend control and trimming.
Constant airspeed climb or descent:  while in a cruise power setting, increase or reduce the throttle, to initiate a climb or descent from current altitude.  Elevator input may be needed during the transition to help establish the correct attitude and avoid oscillations in airspeed.  The aircraft will settle into the climb or descent at the cruise airspeed you have previously used.  Throttle inputs can thence be used to control the attitude of and/or rate of the climb/descent.  No trim will be needed to to alleviate control loads as the airspeed is constant throughout the climb or descent.

The constant speed climb/descent is a bit of a misnomer, because both kinds are flown with constant speed. The former is flown with constant rate while the later with constant power. Also in the constant rate climb/descent, you still have to manipulate power to maintain that rate, because rate of climb/descent equals drag/power.

In one important sense, the pilot doesn't need to do anything to descend: gravity takes care of that all by itself.
A plane descends when its wings produce less lift than it weighs
In order to keep the plane aloft, the pilot needs to keep overcoming gravity - in physics terms, ensure that the aircraft produces more lift than the aircraft weighs.
A wing produces lift when it moves through the air
An airliner produces lift when air flows around its wings, which happens when the aircraft moves forward through the air. By changing the shape of the wings (for example, by extending flaps) or changing the attitude (angle) of the aircraft in the air, the pilot can adjust how much lift the wings produce.
More power = more speed = more lift
One very simple way to descend therefore is to reduce power. This will slow the aircraft down, so the wings produce less lift, and the plane slowly falls.
Why pointing the aircraft down (or up) isn't the way altitude is controlled
Another would be to point it firmly at the ground, but this would not be pleasant or safe, so airline pilots rarely do that.
Although it would seem intuitive that raising the nose will cause the aircraft to climb, and lowering it will cause it to descend, that doesn't necessarily follow.
Other things being equal (i.e. if the thrust produced by the engines does not change) pointing the nose down somewhat will cause the plane to descend, but it will also cause it to go faster.
This is for two reasons:

the potential energy (height) of the aircraft has to go somewhere, so it becomes kinetic energy (speed)
less of the engines' thrust is converted into lift, and more of it contributes to the plane's speed

This extra speed, other things being equal, will in turn cause the wings to generate more lift! Depending on how the controls are set, lowering the nose won't actually cause the plane to descend for very long.
The reverse applies when lifting the nose. Eventually of course if the nose is lifted far enough, although the aircraft will climb rapidly at first, soon it will lose so much speed that the wings fail to produce enough lift to keep it in the air, and it will plummet in what's known as a stall.
So the key overall is engine power, thrust. Smaller and more momentary adjustments will be achieved by moving the aircraft's control surfaces and controlling its angle of attack, but on the whole, a descent involves keeping the plane comfortably level and allowing it to fall very slowly through the sky - as far as possible, so that the passengers don't even feel it.

Seriously wrong on your very first point:  If the wing is producing less lift than the plane's weight, the plane is falling at an accelerating rate!   During any stable phase of flight (including a descent), lift is EQUAL to weight.

"Pitch for airspeed, power for altitude"

@JonStory we discussed that (https://aviation.stackexchange.com/q/2980/1467), it is not completely correct.

I was mostly throwing it in there as a "TL;DR" rather than a "This is the only technique" :)


text:
How does the FAA define day and night?
For the purposes of regulations how do the FARS define daytime? Is it sunrise to sunset, civil twilight, astronomical twilight?
This question was asked before with regards to EASA rules, but FAA was not included.

Related: Is an eclipse considered 'night' for regulatory purposes?

Day and Night for Pilots
As pilots we often talk about night flying and daytime flying meaning when it is dark or light, but for logging time and for currency there are specific definitions that we must pay attention to.
FAR 1.1 General Definitions
Night means the time between the end of evening civil twilight and the beginning of morning civil twilight, as published by the American Air Almanac, converted to local time.
Day is not defined in the FARs but the definition of night implies that it is the time between the beginning of morning civil twilight and the end of evening civil twilight.
The Air Almanac is published annually on CD-ROM but you can find sunset, sunrise, and civil twilight times for specific locations at the US Naval Observatory website.
The time between sunrise/sunset and twilight is 26-30 minutes depending on the time of year. Since you can easily find sunrise/sunset information in newspapers, the weather channel, etc. you can estimate twilight fairly easily.
Currency
§61.57 (b) (1) … no person may act as pilot in command of an aircraft carrying passengers during the period beginning 1 hour after sunset and ending 1 hour before sunrise, unless within the preceding 90 days that person has made at least three takeoffs and three landings to a full stop during the period beginning 1 hour after sunset and ending 1 hour before sunrise, and…
VFR Weather Minimums
Only Class G airspace has different minimums depending on night and day and they use the standard night definition—end of evening twilight to the beginning of morning twilight.
Aircraft Lights
Aircraft lighting is required between sunset and sunrise.
§91.209 During the period between sunset and sunrise no person may 1. operate an aircraft unless it has lighted position lights, 2. park or move an aircraft in an area of an airport where night operations are being conducted unless it is clearly illuminated, has position lights, or is in an area marked by obstruction lights.
Aeronautical Experience Requirement
In order to obtain a private pilot certificate night training is required. The commercial pilot certificate requires solo night flights. In these cases the standard night definition—end of evening twilight to the beginning of morning twilight—applies.
Special VFR
AIM 4-4-6 g. Special VFR operations are prohibited between sunset and sunrise unless the pilot is instrument rated and the aircraft equipped for IFR flight.
Logging Night Flying Time
Logging of night flight should be made in accordance with Part 1 definitions, which is from the end of evening civil twilight to the start of morning civil twilight. This differs from the definition used for night currency.
Summary
Position lights – sunset to sunrise
Special VFR – sunrise to sunset unless instrument rated
Carry Passengers – 1 hour after sunset to 1 hour before
Everything else – twilight to twilight

Just for anyone who’s not familiar with terms like “civil twilight”: timeanddate.com has excellent graphs giving a good visualisation and quick reference for the different official phases of twilight.

The US Naval Observatory has sunrise/sunset and twilight times for the US. http://aa.usno.navy.mil/data/docs/RS_OneDay.php

14 CFR 1.1 defines night as the period between the end of evening civil twilight and the start of morning civil sunrise.  This definition is again referenced in 14 CFR 61.109.  Therefore day is defined as the period between the start morning civil sunrise and the end of evening civil twilight.
That being said the regs also refer to night time as between sunset and sunrise and 1 hour after sunset and 1 hour before sunrise (14 CFR 61.57).
As I understand it, 14 CFR 1.1 is the official accepted demarcation between daylight and night time for the FAA; however it's not used as a standard when say defining when night currency is applicable or when to use exterior aircraft lighting, primarily because of interference from ambient lighting at dusk and daybreak affecting airman prowess during this time.
https://www.aopa.org/news-and-media/all-news/2005/october/11/night-flying-sort-through-the-different-definitions-of-night

Note that 61.57 doesn't actually define night, it just has additional restrictions during that portion of the night that it refers to.


text:
What kind of certifications are required for a plane manufactured for personal use?
If I make an airplane (lets say for research/recreational purposes), what kind of certifications would be required to fly it? Moreover, would I need special permissions to actually fly the airplane? What are laws regarding this to a situation specific to India?

I agree the question was probably too broad. For example a microlight or glider, a single engine general aviation plane, an established design built from a kit or plans, or a totally self-designed experimental aircraft, can all come under different rules and bodies in certain countries.  And we would only get an authoritative answer if a self-builder in, say, India was here to read it.

As Andy pointed out, this question is very broad (even if we're only talking about India). Your starting point should be the Directorate General of Civil Aviation (DGCA) because they can tell you definitively what would be involved in getting a "homebuilt" aircraft approved to fly under Indian law.
Information about this is available on the DGCA website and is broadly similar to the FAA's "Experimental: Amateur-Built" certification requirements:

The aircraft needs to be constructed in accordance with the DGCA's acceptable methods, techniques, and practices. Basically this means you can't use chewing gum as a structural fastener: The aircraft needs to be safe to fly.
The aircraft will be inspected by a DGCA representative prior to being allowed to fly.

Note that the DGCA inspection is mainly looking for "obviously unsafe" conditions - they don't do a teardown inspection so if you used chewing gum as a structural fastener and subsequently that area is covered up by a wing skin the inspector won't know, but you will when the wing falls off on your test flight.

You will need the DGCA to issue you a Certificate of Airworthiness before you can fly the aircraft around - that certificate is contingent on completing required test flights at the airport where the aircraft is based/built.
You will need an appropriate pilot's license (and medical certificate if applicable) in order to fly the aircraft (this is also required to conduct  the Certificate of Airworthiness test flights mentioned previously).


text:
Are pilots generally trained for crosswind landings?
A YouTube footage of a KLM Boeing 777 landing at Schiphol airport in the Netherlands is certainly scary as the plane bumps and weaves and rolls from side to side.

Are pilots generally trained to handle such eventualities (or are such landings common in certain regions of the world?) or was everyone involved including the pilot taking a risk in this case without diverting the aircraft to a nearby safe location?

Of course yes.
Crosswind landings, like the one in the video you linked, are very common. In fact, landings with no wind or only headwind are rare.
There are several techniques pilots are taught during their extensive training to land aircraft when there is crosswind. The Wikipedia article I referenced above lists them. Since your question isn't about them, we won't discuss them.
Certainly, extreme weather situation are not very common. Some parts of the world experience extreme weather more than other areas. Diverting to other airports is not always an option and in some cases, once an airplane is on the approach, going around becomes impossible.

agreed, but this is Schiphol. Lukla is an extreme counterexample, and you don't fly there with a 777.

In the US it is required by law to be trained in cross wind landings.
For large aircraft that require a type rating...

§61.31   Type rating requirements, additional training, and authorization requirements...
...(2) Received a logbook endorsement from an authorized instructor who has found the person proficient in the operation of the aircraft and its systems.
(i) Normal and crosswind takeoffs and landings;
(ii) Wheel landings (unless the manufacturer has recommended against such landings); and
(iii) Go-around procedures.

On a side note cross wind landings are very important since not all airports have 2 runway options. Some large commercial airports will have 2 crossing runways which will allow you to pick the best one for the days winds (they are usually built to the general prevailing winds in the area). This does not mean there will be no cross wind but it does allow you to mitigate it. Smaller airports may only have a single runway (or 2 parallel runways) which means you have no method of mitigation for the crosswind. There are even some big airports that are only single runway due to space  or geographic restrictions.
It should also be noted that airplanes them selves have a demonstrated cross wind component to which they are tested to be safe to land in a cross wind of said velocity. This is not necessary a maximum (although it can be) but it is often used as such.
As for how often this happens that is largely a factor of the airport and the local weather. For example I used to fly out of KPNE they have 2 runway options (6-24 and 15-33) they would use what ever was the best runway for the wind that day unless you needed the precision approach on 24. This made landing there easy (150 x 5000 or 7000 helped as well) as there was never really more than a 15 degree crosswind. I now fly out of KDYL which is a single runway airstrip that almost always has a crosswind, really keeps you on your toes.
Cross wind approaches are perfectly safe and are not out of the ordinary. I have seen some people mistake the phrase Uncoordinated Flight as meaning a sideslipped crosswind landing is unsafe which is incorrect. The plane can be uncoordinated because it is side slipping to the landing which is done deliberately by the pilot.

The answers so far deal with commercial flying, from a recreational perspective pilots are only as well trained as the amount they practice. Commercial organizations generally train their pilots for crosswind landings in simulators, and they usually fly enough to get real crosswinds often enough to keep in practice. Private pilots are trained in crosswind techniques in initial training, keeping good crosswind abilities is up to the pilot once they pass their test. I personally practice crosswind take-offs and landings as often as I can, however I know many pilots who won't fly if there's more than 5 knots across the runway.

very good point. The question is asking about "pilots" in general in the headline, so that would include barnstormers, crop-dusters, tail-draggers, recreational pilots, etc. and you're the first to include that. Somewhat supports my point about the "general" vs. "specific" being a problem, as I've said in another comment on this page. As this group is so general, most people who write "pilots" probably mean "airline pilots" without saying so. But such distinction would be important for a meaningful answer.

Yes, pilots are trained for crosswind landings. I trained on a Cessna 172 as Paso Robles. The video was completely normal. A roll of < 10 degrees is not serious at all, well within a competent pilot's operational abilities. The news story was written by someone who doesn't fly, thought it looked 'scary' and filled 90 seconds with nonsense, IMO.

I'm a little late to the party, but here is my take. In that landing I see turbulence but I don't see an obvious crosswind component.
In any case, dealing with crosswinds is something that happens more often than not when landing (at least at many airports and airfields). So every single pilot has dealt with this since the very first days of basic training.
As for the wing rocking, correcting an off-level wing is probably the very first thing a student learns when getting acquainted with the aircraft's controls. It is completely intuitive for every single pilot.

In steady winds, even when strong or very strong, there is no excuse for bumping around like crazy. You have the "concept" of a "stabilized approach", and only turb is a valid reason to destroy a stabilized approach. In turb that's a different story, but then you still would have to explain why you even attempted the landing. If turb is too strong, it's a good reason to divert. The famous Lufthansa case made the media (and YouTube footage) several years ago where they even had a wing strike on the left side, when tons of other aircraft had cancelled. These two pilots pressed on, seemingly suffering from the eponymous get-home-itis, and you see the result. So ... even turb is not always a valid excuse, because diverting is a safer option (assuming you don't HAVE to land because of low fuel or similar -- but then you'd even have less excuses, because you shouldnt' fly into turb with low fuel, etc.).

Are you saying that this landing was not stabilised?  That landing looks routine to me.  I've experienced far worse than that at Kai Tak.

Given the turb, I'd say it was "stable enough". No, certainly not routine. And I don't mean to be "combative", but what you've experienced is irrelevant to assess this particular situation. Please don't take this sentence personal, take it literally. Personal experiences, which are subjective, don't matter if we want to assess a situation objectively. Others could say "I've never experienced anything so bad", and we couldn't agree/disagree with them, as it's too subjective.

As a passenger, with many hundreds of airliner landings in my experience, it's not subjective at all.  As a pilot, I am perfectly capable of objectively comparing roll, pitch and yaw rates and I have a keenly calibrated ass connected to the airplane which provides feedback.  I have also witnessed many cross-wind landngs from outside, on the airfield (ex-military) and see nothing in this landing that is other than routine,  I would have not been concerned in the slightest to be strapped into the back off that one.

Without a lot more data, it is not possible for observers to call stabilised or not, but I see nothing to suggest that it wasn't.

as I said, I'm not too concerned either. I don't think anything was ever unsafe. With "not routine" I mean the weather conditions. As I said, the turb was strong enough to consider diverting. To make it more objective, one could now the max crosswind components and max gust factor for which the 777 is still certified, with the actual weather numbers ... probably not doable, we don't have that data. But to me it seems gusty enough to approach the max gust factor for the 777 and then divert. "non routine" refers to weather.

@Simon: precisely. more data would help. Actual gust factor against max 777 gust factor, to better assess if diverting would have been better.

@AndreasLauschke: What was the Lufthansa flight?

just YouTube for "Lufthansa wing strike". You'll get plenty of hits. Don't forget the background: most flights to this airport cancelled due to the heavy squalls.

Thanks, found it. Note that this was not entirely due to pilot error, but the single sided gear touchdown put the plane into 'ground mode', which resulted in halving the aileron deflection available through the pilot's sidestick - so the pilots lost half their control authority as soon as the gear touched the runway.

I consider it pilot error, specifically a judgment error, as they shouldn't have attempted the landing in the first place. Most other planes diverted too, and ground mode resulting in halving the aileron deflection must be part of the decision process of the PIC when landing in such squalls. Such loss of control authority must be part of the decision process -- it's not that plane malfunctioned, and as PIC you KNOW that this would happen in ground mode.

That's true, the ground mode should have been part of their decision, but they apparently didn't know it could happen with a single gear touchdown: "It is impossible to clarify whether the pilots would have taken a decision for a go-around procedure earlier, had there been a risk evaluation that included aircraft system behaviour, then unknown to the crew,"

ah, interesting. Thanks for the details.


text:
Why doesn't ice form on the fuselage?
Ice forms on the wings and instrument probes and vanes, but why not on the fuselage? If the temperature of the air is the same, why does the ice form on the wing but not on the fuselage?

Related: Why would a canard wing be more prone to icing than a stabilizer?. Temperature is not the only condition for icing, pressure plays a role. See this guide on icing: Aircraft Icing Handbook

My guess is ice does form on fuselage but it is not as critical to aerodynamic as ice forms on wings. https://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/deicing/media/standardized_international_ground_deice_program.pdf

It does.  I've seen it (on a 172, while doing instrument cross-country).

Small planes sometimes have addition heated plate of the windows for this. On big airplanes front windows are heated for this and bird strike protection

Ice doesn't form on the fuselage because pilots go out of their way to avoid atmospheric conditions conducive to ice accretion.

It does, but there is much less of it on the fuselage than on the wing.
There are two ways how ice is accumulated on the aircraft's structure:

When flying through air containing supercooled water droplets, the water will freeze on impact. It does not make much of a difference whether the water impacts the fuselage nose or the leading edge of the wings and tail surfaces: It will form a sheet of clear ice.
When flying through moist air at a temperature close to freezing, the pressure loss of the air flowing around any obstacle will cool it down, so the moisture condenses and, if temperature allows, will form ice accumulations. Those in turn exacerbate the suction peaks, leading to more ice being collected.

The wing's leading edge shows the most pronounced suction peaks, so they will collect most ice. However, if the icing conditions are right, the fuselage nose will also pick up it's share of ice. Along the length of the fuselage, pressure is similar to ambient, so it will collect ice only when sitting on the ground in freezing rain.

Iced engine nacelle in the NASA Lewis (now Glenn) Research Center icing research tunnel (picture source). Here, water is sprayed into the tunnel and forms supercooled droplets.
In both cases icing has nothing to do with the boundary layer - with supercooled water it is simple ballistics, while the second case of ice accumulation is dominated by the pressure of the flow around the aircraft.

In order to answer you properly I need to first introduce firstly the concept of boundary layer. When an airplane is flying over the air in normal conditions (I mean, usual high Reynolds number), the air flows cretes an small layer around the airplane that is call boundary layer (image source Portland State University)

The previous figure gives you an sketch of how is the boundary layer around an airfoil that is similar to the figure you will see around the airplane. Notice the following behaviours of the air:

The boundary layer grows downwash.
The boundary layer is really thin at the beginning.
The air flow (the inviscid flow...) follows the shape of the limit of the boundary layer, not the shape of the airfoil.

Now, let's say the air contains some water drops. Depending on the size of the water drops they can behave following the air or like bullets following the an straight path. In the reallity the drops have an intermediate behavior, having some inertia and taking some time to adapt to the flow.
Based on that, some drops following the streamlines of slighly over or down the airplane will almost follow the streamlines flying over the boundary layer and not pouring over the surface.
However, some drops will impact directly over the surface of the airplane in what is called "stagnation point", once over that surface they will behave like an humid surface moving in the air... the drops will expand along the surface and eventually leave the surface, in that process due to the air temperature and the surface heat exchange ratios some ice will be formed.
With the previous explanation we can understand why ice is not formed in the rear part of the fuselage, simply because the boundary layer is "protecting" it and the water accumulated in the front is simply not reaching the rear part.
In order to find locations where you can find ice in an airplane, just look for stagnations points (where the flow "impacts" in a simplified way) and the surrondings. Where do we have this areas?

Leading edges of wings (image source AirDorrin)

Engine inlets ( image source NASA)

Instruments (image source AviationWeather)

Rarely front windows (image source  flyjoe180 at Wings over new Zeland)

Front fuselage (did not find any picture).

Of course, having the airplane on ground removes the "protection" of the boundary layer, leaving the airplane exposed to any ice creation.


text:
What does one do when the weather report has a bogus altimeter setting?
I saw a METAR for a nearby airport that had A2248 ... SLPNO in it with no maintenance indicator.  Is the SLPNO a sign that the altimeter setting in the METAR is untrustworthy as well?  How else does one get the altimeter setting (assuming ATIS is drawing from the same, messed up data source that the METAR is -- this is an RMK AO2A METAR), or is one grounded until the AWOS reading is fixed?

Could you post the METAR in full?

Since SLPNO means that the surface pressure is unavailable, how could it mean anything else except that the altimeter setting is unreliable?  Are you asking why is didn't include a maintenance indicator, or what does SLPNO mean?  I'm guessing that 2248 is the highest possible measurement.

@Simon I think his main question is what to do about the situation. How to get the correct reading.

If you are on the ground at the field in question could you not just set the alt to read field elevation? Then you would have the correct pressure dialed in.

@TomMcW Yes, but a strict legal reading will show that method is only allowable if your aircraft is not radio equipped. All aircraft flying below 18,000, except aircraft not equipped with a radio, are required to set their altimeter to the current reported altimeter setting of an appropriate available station. See 14 CFR 91.121.

@Steve -- if you can get me a place that has an archive of METARs for a US airport going back several days, yeah, I can get you the METAR...

@JonathanWalters -- I wonder if you can substitute some other airport's altimeter setting in this case...

@unrecognizedfallingobject Absolutely. See 14 CFR 91.121, the requirements are fairly straightforward.

@JonathanWalters -- that sounds like an answer then

We might speculate why the METAR is giving innaccurate data, but the question asks, "What should one do..."
I will take the liberty of inferring the question to be "what should one do if one is unable to obtain an altimeter setting for the airport from which he or she is preparing to depart?" Note that this question could be asked due to an airport with a faulty weather reporting system (as in the question above), an airport without weather reporting at all (quite common, for example: D42 or S68), or an aircraft that is not radio equipped.
I will further take the liberty of answering from what I know: the FAA regulations.
I will point out that it is the pilot's responsibility to be familiar with all available information and this should include a thorough weather briefing whenever possible.
Under the FAA's jurisdiction, the relevant regulation is 14 CFR 91.121 (a) (1):

(a) Each person operating an aircraft shall maintain the cruising altitude or flight level of that aircraft, as the case may be, by reference to an altimeter that is set, when operating—
(1) Below 18,000 feet MSL, to—
(i) The current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft;
(ii) If there is no station within the area prescribed in paragraph (a)(1)(i) of this section, the current reported altimeter setting of an appropriate available station; or
(iii) In the case of an aircraft not equipped with a radio, the elevation of the departure airport or an appropriate altimeter setting available before departure

(Since all airports and terrain in the US are below 18,000 MSL, this applies to takeoff; the rules governing flight above 18,000—14 CFR 91.121 (a) (2)—do not apply to our question. "Operate" is defined in 14 CFR 1.1.)
We can go through this like a flowchart:
If "the current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft" is available, use that.
(Note that this could include current reported altimeter settings obtained by radio (ATC, flight service, or a nearby airport), phone call (briefer or AWOS), internet, or any other method that would procure the needed data.)
If no such station is available, then use "the current reported altimeter setting of an appropriate available station."
Now, if the aircraft in question is not equipped with a radio, then (and I would read technically only then) the pilot is permitted to set the altimeter to "the elevation of the departure airport or an appropriate altimeter setting available before departure."
Now, that being said, if a pilot is in the middle of the Idaho backcountry at Wilson Bar (C48), or on the face of an Alaskan glacier, with no cell reception and no real way to acquire a current reported altimeter setting despite being in a radio equipped aircraft, then actual practice will be to set the altimeter to field elevation and get on with it. However, the requirement to use a current reported altimeter setting remains, and should be acquired at the first available opportunity.

If on the ground set your altimeter to indicate the field elevation and the altimeter pressure indicator will be adjusted with it.
If in the air ask a controller for it.  Most towers I have been in have their own air pressure indicators so that they can advise pilots of the correct altimeter setting for landing.
If uncontrolled ask the airport "radio" for it.  "Radio"is a term used for anyone monitoring.


text:
Why doesn't a single engine airplane rotate along the longitudinal axis?
As far as I know, the tail rotor in helicopters prevents the aircraft from turning in the opposite direction that the main blades turn (due to Newton's third law). On the other hand, torque in single-engine airplanes makes them drift away from the center of the runway during take-off (which must be compensated by using the rudder). Now, my question is: once in the air, why doesn't this torque make the whole aircraft spin along the longitudinal axe? Perhaps the engine's power isn't enough to exceed the resistance of the wings against the air?

But it does.  I torque rolled (unintentionally) a T-28 when practicing Approach Turn Stalls: the combination is both low airspeed, and a very powerful engine, and (in my case) insufficient rudder control to counteract the torque roll. (My instructor had a few acid comments on the whole deal ...)

This question has earned more upvotes than the one which some people thought already has answers. That says it all.

First, it's about torque, not power.  A helicopter rotor has a large amount of torque at a relatively low RPM.  A single engine airplane has much less torque at a higher RPM (Power = Torque X RPM).  On top of that, for a craft of similar size, the helicopter will have much more power (it has to lift the copter directly.)  So the helicopter has to deal with torque levels several multiples higher than that of a single engine aircraft.
As to the solution, most single engine aircraft have the vertical stab offset by a small amount to generate a counter force to the torque.  If you look at some high power aircraft such as the P-51, it's a noticeable offset. And that's set for cruise power.  Takeoff power requires additional rudder input.
It should also be noted that for smaller aircraft, P-factor is a bigger turning force during climb than engine torque.

P-factor is very different effect from torque!

@Jan Hudec. Yes it is. But it does require rudder to counter and for most small a/c it is the dominant cause of the turning tendency.  Control of the plane requires addressing all forces on the plane.  So you just can't say x is there to compensate for y.  It may also compensate for f, g, and q.

Yes, control requires addressing all forces on the plane. But the question is about one of them and you are describing how the other is compensated for.

A Cessna 172 doesn't have enough torque to counteract the stabilizing effect of the wings and empennage. The Grumman F8F Bearcat had a reputation for giving wild rides if power was applied too quickly at low airspeed. My understanding is that you could torque roll an F8F ON THE GROUND without moving (much) - just jam the throttle forward from idle and watch how fast 2000 horsepower can pick an airplane up off the ground and flip it over.

"torque roll an F8F ON THE GROUND" - do you happen to have a link to a video?

Often times propellor driven aircraft have differential angles of incidence built into their wings such that they generate a counter torque to the engine.  Some turboprops also use differential exhaust stacks to make use of reactive thrust from engine exhaust to counter engine torque.